Draft control means for fuel burners



Dec. 14, 1948.

W. S. LANDON DRAFT CONTROL MEANS FOR FUEL BUENERS 2 Sheets-Sheet 1 Filed April. 28, 1944 FIG.3

INVENTOR.

62 mm A M M ATTORNEY FIG. 4

Dec. 14, 1948. WI 5, LA DON 2,456,131

DRAFT CONTROL MEANS FOR FUEL BURNEHS Filed April 28. 1944 2 Sheets-Sheet 2 F I G. 6 INVENTOR.

Patented 14, 1948 DRAFT CONTROL MEANS FOR FUEL BUBNEBS Walter s. Landon, Detroit, Mich assignor to Detroit Lubricator Company, Detroit, Mich a corporation of Michigan Application April 28, 1944, Serial No. 533,119

14 Claims. 1

The invention relates to fuel burning systems and it has particular relation to the automatic control of draft or air supplied to the burner.

While the invention is applicable to different fuel burning systems, its purpose may be illustrated particularly in connection with a fuel burning system which normally operates under high and low fire conditions. In a system of this character wherein a pot type burner is employed, a. relatively large quantity of oil is supplied to the burner under high fire conditions as when heat is required and then between the high fire stages, a relatively small quantity of fuel is supplied so as to provide a small or low fire. Under the same conditions respectively, a blower operates at relatively high speed for supplying forced air or draft to the burner in the high fire stage and at a reduced speed for supplying less draft in the low fire stage. It is further desirable in a system of this character that in the event the blower ceases to operate that the natural draft supplied to the burner will be sufflcient to support a low fire condition, although in this connection it is to be understood that the forced draft is preferable and that it is only in the event the forced draft ceases that operation under natural draft conditions would occur.

One object of the present invention is to provide a fuel burning system such as indicated, wherein the size of the inlet opening to the blower will be controlled by air pressure at the discharge side of the blower.

Another object of the invention is to provide a system of the last mentioned character which will avoid a condition wherein air at the discharge side of the blower would escape from the duct before reaching the burner so as to thereby maintain desired draft conditions between the blower and the burner.

Another object of the invention is to provide a system such as mentioned wherein the size of the inlet to the blower is increased when the blower is operating at its higher speed, is reduced when the blower is operating at its lower speed and is automatically increased when the blower ceases to operate.

Another object of the invention is to provide a damper for the inlet side of the blower which is moved automatically by pressure controlled means at the discharge side of the blower when the blower is operating and is movable inde pendently of the control means when the blower is not operating.

Other objects of the invention will become apparent from the following specification, from the drawings forming a part thereof, and from the claims hereinafter set forth.

For a better understanding of the invention reference may be had to the accompanying drawings wherein:

Figure l is a diagrammatic view illustrating a fuel burning system constructed according to one form of the invention:

Figure 2 is a fragmentary side elevational view illustrating a damper control constructed according to the invention and embodied in Flaure 1 with the damper in a position supporting a low fire condition under forced draft;

Figure 3 is a view similar to Figure 2 illustrating the position of the damper control under forced draft supporting a high fire condition;

Figure 4 is a. similar view showing the position of the damper control with a natural draft condition;

Figure 5 is a plan view of the blower, air duct and damper control means; and

Figure 6 is a side elevational view of the arrangement shown by Figure 5 with certain parts broken away for the purposes of clarity.

Referring to Figure l, a burner is indicated at ill and comprises a pot Ii adapted to receive fuel oil, for instance, through a supply line I! leading to a float chamber, a part only of which is shown at IS. A valve stem ll movable vertically in the float chamber It has a lower reduced end movable through an opening ii in the lower wall of the chamber and such lower end of the stem has a V-shape groove or slot It. When the stem is raised sufficiently, oil flows through the opening l5 at a relatively large rate and when the stem is in its position shown, the V-shape slot I! reduces the supply of oil to a relatively small amount. Hence, with the stem raised to supply a large quantity of oil, a high fire may be maintained in the burner and with the stem in its lower position, as shown, a low fire is maintained in the burner.

A spring It on the valve stem and abutting an intermediate wall ll of the float chamber at one end and a collar IS on the stem at its other end, normally urges the stem to a fully open position for supporting high fire. Reverse movement of the stem for a low fire condition is effected by a thermal element 2| which may be in the form of a bi-metallic member. This bi-metallic member abuts a shoulder. on the upper end of the stem and in the absence of the heat, the bi-metallic element holds the stem in its lower or low fire position. An adjustable screw 23, threaded across:

through an upper wall 24 of the float chamber serves to limit upward movement of the valve stem.

Movement of the valve stem automatically from one position to the other is governed by the action of a thermostat 25 having a contact 2| adapted to engage in contact 21. This thermostat is in a low voltage circuit including the low voltage side 28 of a transformer and the circuit includes a heating element 29 which may form part of the thermal element 2|. Hence, when the thermostat is moved to close the circuit the bi-metallic element 2| moves upward through the action of heat so as to open the valve stem and when the thermostat opens the circuit the thermal element through its own inherent resiliency returns to its initial position against the action of the spring II so as to move the valve stem to its lower position. The thermal element 2| may have one end rigidly fastened to the float chamber side wall so that its movement upwardly and downwardly will be governed by changes in temperature.

Air is supplied to the burner I! by means of a duct 30 leading to a casing 3| surrounding the pot ii, and from this casing air is led into the pot by means of openings 32. At its upper end the pot ii is open, as indicated at 34, and this opening is normally connected to a flue. At its opposite end, the duct 30 is connected to a blower casing 34, having, as best shown by Figure 5, a blower therein. This blower may be of the usual centrifugal type and air enters the blower casing through an inlet duct 36 connected to the side of the blower casing.

The blower is driven by a motor 31, shown by Figure 5, and the motor is connected to wires 38 and 39, which are in turn connected to a lead-in wire 40 and a movable switch element 4|. The high side of the transformer previously mentioned is indicated at 43 and is connected to the lead-in wire 40 and a second lead-in wire 44. The motor is adapted to be operated at what may be termed full speed and half speed for high fire and low fire conditions, respectively. For operating the motor at high speed, a switch element 48 adapted to contact switch element 4| is provided and this switch element 46 is connected by a wire 41 to the end of the transformer coil 43. A second switch element 49 also adapted to contact the switch element 4| is'connected to a wire Bll which is in turn connected to a central point on the coil 43. It follows that ii the switch elements 4| and 46 are in contact the motor will operate at full speed. whereas if the switch elements 4| and 49 are in contact, the motor will operate at substantially half speed. At a point indicated at 53, the switch element 4|, is pivotally mounted so that it may be moved selectively into contact with the switch elements 46 and 49.

For moving the switch element 4| downwardly at the same time that the valve stem |4 moves downwardly, an adjustable bushing I56 is threaded on a stem 51 slidable through openings in the walls of the float chamber and this bushing has a shoulder 58 engaging the thermal element 2|. At its lower end, the stem 41 contacts a projecting portion of the switch element 4| and from this it follows that the thermal element in moving downwardly will close the circuit to the motor so that the same will operate at half speed. As a part of the arrangement provided to move the able support which may be in the float chamber. Assuming that the parts are as shown, the downward pressure of pin 81 as influenced by the thermal element 2| holds the parts in the positions shown. As this pressure or force is relieved when the thermal element 3| begins to move upwardly the forces become unbalanced and the switch arm 4| begins to move slightly upwardly. Then as the pin 40 shifts farther from alignment with the pivot ll, the arm 54 acts with rapidly increased force and moves the switch arm 4|, pin SI and thermal element 2| upwardly so as to cause arm 4| to contact arm 46. Conversely, when thermal element 2|, due to cooling, begins to move downwardly, the movements are reversed and contacts 4| and 49 are closed. Other means could be used to cause arm 4| to move from one contact to the other as the thermal element 2| is moved, as will be understood by those skilled in the art.

At its upper end the pin 51 is provided with a spacer sleeve 10 and adjusting nuts II and I2 disposed respectively at the lower and upper sides of the upper wall of the float chamber so as to provide limits governing movement of the pin and downward movement of the thermal element.

It should now. be evident that depending upon whether or not a space heated by the burner requires heat, the thermostat 25 will operate so as to cause operation of the burner at high fire, or operation of the burner at low fire. It should also be evident that with the burner operating at high fire the blower is being driven at its high speed and that when the burner is operating at low fire the blower is being driven at substantially half speed. While the pressure at the discharge side of the blower will be less with the blower operating at low speed, the forced draft for the burner will still be greater than desired because it is impractical to sufllciently reduce the speed of the motor. There- 40 fore, a damper is ordinarily required at the inlet side of the blower. The present invention is concerned with the provision of a damper which will control the air inlet in accordance with the pressure at the discharge side of the blower so that the proper draft will be obtained for both high and low fire. It is further concerned with the operation of this damper so as to obtain a desired natural draft in the event the blower ceases to operate.

Directing attention to Figures 5 and 6 in particular, the damper for the inlet is indicated at It and it is pivotally mounted on a central crank portion ll of a pin 1'! pivotally extending through diametrically aligned openings in opposite sides of the inlet duct 30. The crank portion 16 is parallel to the pin TI and from this it follows that the damper may swing about the axis of the pin 11 or about the axis of the portion 18. At a point below the pin 11,9, counterweight 8B is secured to the damper by means of a -pin or rivet element ill and the counterweight may tend to swing the damper about the axis of portion 16 in one direction or another depending upon the position of the parts.

The pin 1'! extends beyond the side wall of the inlet 36 and into a casing 43 fastened on the upper side of the duct Ill at the discharge side of the blower. Within the casing 84, the pin 11 is secured to a movable wall element or blade SI, and this blade rather closely nts the side walls of the casing 88 so as to prevent any undesirable leakage of air past the edges of the blade. In this connection it will be observed that one wall 8B of the casing 83 is curved so that the edge of the blade 85 will continue in close relation to the wall during any swin ing movement of the blade. That edge of the blade next to the blower similarly maintains a close relation to the upper surface of the blower casing. Adjusting screws 81 and 88 threaded through the upper wall of easing II limit the movement of the blade 85 in both directions. Air above the blade 8! is allowed to escape freely through an opening 89 in the casing while below the blade 85 air within the duct III may act against the blade through an opening 98 in the upper wall of the duct.

Now referring to Figs. 2, 3, and 4, the damper and controlling means therefor are so designed and related as to obtain certain conditions of draft depending upon whether the blower is operating at half speed, full speed, or is not operating. Initially, it is to be noted that movement of the damper and the blade 85 together and relatively depends upon difierent conditions or factors such as weight and varying position of the counterweight, weight of the damper and blade, amount the damper is open and pressures against both the damper and blade. These factors and the manner in which the damper operates may best be understood by describing the action in different stages of draft control.

With particular reference now to Figure 2, the blower is operating at half speed. In this stage, the weight of the blade 85 multiplied by its effective moment arm relative to pin 11 is greater than the weight of the counterweig t 80 multiplied by its moment arm relative to pin-I1 plus the air pressure in duct 30 multiplied by the area of the blade 85. Weight of blade 85 or area thereof is intended to mean the weight or area of that part of the blade at the right side of the pin 'I'I minus the weight or area of that part of the blade at the left side of the pin. It is to be understood too that the pressure at the outerside of the damper holds it against the pin 11 and that when the parts are in this relation, the pin is djametrical to the circular periphery of the damper. With reference to the action of gravity, it is to be understood that the upper wall of duct 30 is horizontal and that the vertical, therefore, is in 90 relation thereto. Therefore, if W=weight of the counterweight, M=the weight of blade 85, d=moment arm of W about 11, p=pressure in duct 30, A=area of 85, and r=moment arm of M and A about 11, we

ave:

Mr is greater than Wd+pAr Now, when the blower goes to full speed, more air will flow past the edges of the damper and the pressure in the duct will increase. The parts are so related that this increase will cause the blade 85 to move and, therefore, at the time movement be ins:

Mr is less than wd-i-piAr Mr. is greater than Wd1+Apar where p: is the new pressure and d1 the moment arm of W in Fig. 3. The blade now begins to drop and closing of the damper begins. As this occurs, the pressure in the duct decreases and the moment arm ofW increases, but the decrease in pressure is such that Mr continues to be greater than the sum of the opposing moments of force and the blade and damper return to their positions shown by Fig. 2.

If the blower now ceases to operate, the pressure on blade would decrease and hence the blade would remain in position. However, as pressure on the outer side of the damper decreases due to decrease in air movement, the counterweight W, acting through its moment arm about 18, acts to swing the damper about the latter overcoming the net weight of the damper acting through its moment arm about 18 plus the effect of any slight air pressure acting against the outer side of the damper. As a result, the damper swings to a position seen in Fig. 4 where the forces are balanced and a larger supply of air is allowed to flow by natural draft so as to support a natural draft fire.

When the blower goes on and at half speed,

the air pressure differential across the damper increases and the latter begins to move about the portion 16. As the damper moves, the differential in pressure increases and hence the damper is urged towards closed position about the portion 16 with an increasing pressure. While the moment arm of the counterweight is increasing as the damper moves, the increase is not as great as the pressure increase and the damper is quickly moved to a position against the central pin 11. If the blower goes on at full speed or goes from half to full speed, pressure on the blade 85 effects a shift of the crank arm and damper to the positions shown by Figure 3.

In connection with the foregoing, other factors are involved too, such as the weight of the rivet or pin connecting the counterweight to the damper and the somewhat changing moment arm of the blade, weight of the damper, friction, but manifestly these can be taken into consideration so that the damper will function as outlined. Such other factors may be easily included in the calculated design and in fact may be so minor that they may be neglected.

The system described includes a natural draft position of the damper in the event the blower ceases to operate. This draft is preferably such as to support a low fire condition, although this natural draft would support a less emcient consumption of fuel even in thehigh fire fuel flow stage. In order to reduce the fuel flow to the low fire rate under these conditions. a safety switch may be used, such as disclosed in my Patent No. 2,344,946 wherein a thermal element in the air duct adjacent the blower is constantly heated by an electric heating element and as long as the forced draft is sufficient, the air stream cools the thermal element to a certain degree and maintains it in a certain position. However, if the forced draft fails the thermal element heats up and breaks a low voltage circuit. A thermal element of this character may be used in the duct 30 herein in conjunction with a switch which may be placed in the circuit of thermostat 25 and heating element 29. Hence, if the forced draft ceased or became too low, the circuit through the heating element 29 would be broken if at that time completed. and the valve stem I4 would be moved to low fire fuel flow position.

Operation of the system as described occurs automatically and without interference with draft conditions in the duct between the blower and burner. It follows that the control does not interfere with pressure conditions across the burner. The desired pressure drops across the burner can thus be maintained even though the hue pressure varies.

Although only one form of the invention has been illustrated and described in detail, it will be apparent to those skilled in the art that various modifications may be made without departing from the scope of the appended claims.

What is claimed is:

l. A fuel burner air supply device, comprising an air supplying duct for connection to a burner and having an air inlet, a blower in said duct, a damper in the inlet side of the duct and having an open position, means biasing said damper to said open position when the blower is idle, a movable member acted upon by the pressure in the duct at the discharge side of the blower, and lost-motion means connecting the damper and member so that inlet air pressure created by the blower can take up the lost-motion and move the damper toward closed position without movement 01' said member, said member acting upon predetermined increased pressure acting thereon to move said damper toward open position.

2. A i'uel burner air supply device, comprising an air supplying duct for connection to a burner and having an air inlet, a blower in said duct a movable member acted upon by the pressure in said duct at the discharge side of the blower, a damper in the duct at the inlet side of the blower, and means operatively connecting the damper and member so that movement of the latter by pressure variation effects movement of the damper. said connecting means including a lostmotion connection and a counterweight such that the damper is moved automatically by the counterweight independently of the member to change the size of the inlet opening when the pressure acting on the member reaches a predetermined low point.

3. A i'uel burner air supply device, comprising an air supplying duct adapted to be connected to the burner and having an air inlet, a blower in said duct, a movable member acted upon by the pressure in said duct at the discharge side of the blower, a damper in the duct at the inlet side of the blower, and means operatively connecting the damper and member so that when the pressure increases to a predetermined amount the damper is moved in an opening direction to a predetermined position and when the pressure is reduced to a, predetermined amount the damper moves in a closing direction to a predetermined position, and means operable on said damper and actin when the pressure is further reduced to a predetermined amount to move the damper in an opening direction to increase the size of the opening.

4. A fuel burner air supply device, comprising an air supplying duct for connection to a burner and having an air inlet, a blower in said duct, a movable member acted upon and movable by changes in the pressure in said duct at the discharge side of the blower, a damper in the duct at the inlet side or the blower, means operativeiy connecting the damper and member so that the former is moved alternately from one predetermined position to another depending on changes between high and low limits of pressure at the discharge side of the blower while the latter is operating, and means for moving the damper to an intermediate position when the blower ceases to operate.

5. A i'uel burner air supply device, comprising an air supplying duct adapted to be connected to the burner, a blower in the duct, said duct having an inlet on the inlet side or and for supplying air to said blower, a damper in said inlet, means mounting the damper i'or swinging movement about two axes so that it may swing about one or the other, means controlled by pressure in the discharge side of the blower for moving the damper about one axis alternately between different positions depending on changes in the pressure between high and low limits determined by variation in the operation of the blower, and means for swinging the damper about its other axis in the event the pressure drops below its lower limit as when the blower is not operating.

6. A fuel burner air supply device, comprising an air supplying duct adapted to be connected to the burner, a blower in the duct, said duct having an inlet for supplying air to the blower, a damper in said inlet, means mounting the damper for swinging movement about two axes so that it may swing about one or the other, means controlled by pressure in said duct on the discharge side of the blower and operatively connected to and acting through said mounting means for moving the damper about one axis alternately between diiierent positions depending on changes in the pressure between high and low limits determined by variation in the operation of the blower, and means for swinging the damper about its other axis in the event the pressure drops below its lower limit as when the blower is not operating.

7. In a fuel burning system having a burner, an air supplying duct connected to the burner, a motor driven blower in the duct, an inlet on the blower, a damper in said inlet, means mounting the damper for swinging movement about two axes so that it may swing about one or the other, means controlled by pressure in the discharge side of the blower for moving the damper about one axis alternately between diflerent positions depending on changes in the pressure between high and low limits determined by variation in the operation of the blower, and means for swinging the damper about its other axis in opposition to air pressure on the inlet side of the damper when the latter pressure reaches a predetermined amount.

8. A fuel burner air supply device, comprising an air supplying duct adapted to be connected to the burner, a blower in the duct, an inlet on the blower, a damper in said inlet, means mounting the damper for swinging movement about two axes so that the damper may be swung about either axis, said means comprising a shaft journaled in the walls of said inlet and having a crank portion. said damper being pivoted on said portion, means governed by air pressure on the inlet side oi the damper for swinging the latter about said crank portion, and means responsive to blower output to swing said damper about said shaft.

9. A fuel burner air supply device, comprising an air supplying duct adapted to be connected to the burner, a blower in the duct, said duct having an inlet for supplying air to the blower, a damper in said inlet, means mounting the damper for swinging movement about two axes so that the damper may be swung about either axis, and means governed by air pressure on the inlet side 01' the damper for swinging the latter about one axis, said means comprising a counterweight acting to swing the damper towards an open position when the latter is substantially in closed 10. A fuel burner air supply device, comprising an air duct, a blower in the duct, an inlet for the blower, an auxiliary casing on the duct at the discharge side of the blower, a pivotal blade in said casing and extending on opposite sides of its axis and having all of its marginal edges closely fitting the sides of said casing throughout blade movement so as to substantially eliminate air leakage past the edges of the blade, the space at one side of the blade being open to the duct and the space at the other side of the blade having an exhaust opening, means engageable with one side of said blade on the opposite sides of its axis to limit movement of said blade in opposite directions, and means in said inlet and operatively connected to the blade for controlling air flow through the blower in accordance with movement of the blade as effected by air pressure in the duct.

11. A fuel burner air supply device comprising an air supply duct including a blower housing interposed between an inlet duct portion and an outlet duct portion for connection to a burner, a blower wheel in said housing, an air pressure casing on and communicating with said outlet portion, a shaft extending through said casing, a blade fixed against rotation on said shaft within said casing and responsive to pressure in said outlet portion, said inlet portion extending parallel to said outlet portion and diametrically receiving said shaft, and a damper mounted on said shaft within said inlet portion and movable by said blade.

12. A fuel burner air supply device comprising an air supply duct including a blower housing interposed between an inlet duct portion and an outlet duct portion for connection to a burner, a blower wheel in said housing, an air pressure casing on and communicating with said outlet portion, a shaft extending through said casing, a blade fixed against rotation on said shaft within said casing and responsive to pressure in said outlet portion, said blade having portions extendin on opposite sides of said shaft, means engageable with said blade portions to establish limits for movement of said blade in opposite directions, said inlet portion extending parallel to said outlet portion and diametrically receiving said shaft, and a damper mounted on said shaft within said inlet portion and movable by said blade.

13. A fuel burner air supply device comprising an air supply duct including a blower housing interposed between an inlet duct portion and an outlet duct portion for connection to a burner, a blower wheel in said housing, an air pressure casing on and communicating with said outlet portion, a shaft extending through said casing, a blade fixed against rotation on said shaft within said casing and responsive to pressure in said outlet portion, said inlet portion extending parallel to said outlet portion and diametrically receiving said shaft, said shaft having a portion extending within said inlet duct portion and including a crank arm, a damper pivoted on the air inlet side of said crank arm and movable by inlet air pressure into engagement with said shaft portion, and means urging said damper away from said shaft portion and toward open position.

14. A damper comprising a crank arm having two pin or shaft portions with their axes in laterally offset parallel lines, one pin or shaft portion being adapted to be journalled in an air duct with the other portion positioned within the duct to swing around said one portion, a damper swingably connected to and on the other pin or shaft portion so that said damper is movable concentrically and eccentrically about said one portion, and means for rotating said crank arm.

WALTER S. LANDON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,830,575 Tiernblom Nov. 3, 1931 1,954,125 Gerow Apr. 10, 1934 2,149,934 Carter Mar. 7, 1939 2,163,706 Sayers June 2'7, 1939 2,231,885 Nelson Feb. 11, 1941 2,252,425 Crooker Aug. 12, 1941 Certificate of Correction Patent No. 2,456,131. December 14, 1948.

WALTER S. LANDON It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 8, line 75, claim 9, after closed insert the word and period position;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Ofiice. Signed and sealed this 2nd day of August, A. D. 1949.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

